Myth: The black/white IQ gap is 15 points and growing.
Fact: The black/white IQ gap is 7-10 points and shrinking.
Summary
Nationally representative IQ tests show a black/white IQ gap
of 7 to 10 points. Academic achievement tests, for those who consider
them valid measurements of IQ, show an average gap of about 10
points. In general, these tests show the gap is being reduced
about two and a half points a decade. The Bell Curve flouts
all this evidence on the basis of a single study, its own flawed
analysis of the National Longitudinal Survey of Youth.
Argument
Among scientists, it has been common knowledge that
both black and white IQs have been rising over the decades, with
black IQs converging upwards towards whites. This fits nicely
with America's rising standard of living, which has been rising
somewhat faster for blacks, thanks to the Civil Rights movement
and other anti-poverty measures.
The authors of The Bell Curve, then, face an uphill battle
in trying to prove that black and white IQs are not converging,
but diverging. They attribute this divergence to "dysgenesis,"
which supposedly results when dull people interbreed. In fact,
they assert this downward trend in spite of the famous "Flynn
Effect," which has been raising IQs for all people and all
classes world-wide, about 3 points per decade.
In a second departure from scientific consensus, the authors also
maintain that the IQ gap between blacks and whites is 15 points,
an usually high figure. But this is not what four major IQ tests
for children have found:
Black/white IQ gap in major IQ tests (1991) (1)
Ravens Standard Progressive Matrices 7 points
Kaufman Assessment Battery for Children 7
Stanford-Binet IV (two separate studies) 10
The authors of The Bell Curve note these numbers, but dismiss
them. The Kaufman-ABC results, they claim, suffer from statistical
problems. (2) Even granting them their objection, however, still
leaves three major studies showing a 7 to 10-point gap, not a
15-point one.
Why do the authors discount both the Flynn Effect and these test
results in their assessment of black IQ? Because of a single
study: their analysis of the National Longitudinal Survey of Youth
(NLSY). The NLSY has tracked the lives of 12,000 young people
since 1979, at one point giving them an Armed Forces Qualification
Test (AFQT). But The Bell Curve's analysis of the NLSY
data is deeply flawed. First of all, the AFQT isn't even an IQ
test. "This is an achievement test," said Halford Fairchild
of the American Psychological Association said, in its authoritative
review of The Bell Curve. "It shows the extent to
which you've benefited from school. To assert it's a proxy for
IQ is a big lie." (3)
Even if we accept the AFQT as an IQ test, however, the authors
still commit serious errors analyzing it. One of the best-known
critics of their methodology is psychologist Richard Nisbett,
whose arguments follow here. (4) Herrnstein and Murray's comparison
of black and white IQs did not follow the changing IQs of children
over a period of time (the most reliable method), but differences
of IQ between mothers and children at a fixed point in time (which
introduces all sorts of statistical complications). Herrnstein
and Murray found that the black/white IQ gap among mothers was
13.2 points, but among their children was 17.5 points. (5) This
four-point increase forms the basis of their claim that the black/white
IQ gap is growing.
However, the study itself is unrepresentative of the nation at
large; the average IQ of the children was 92, significantly below
the national average of 100. The reason is because the women in
this long-term survey had not finished their childbearing years,
so all the children in the study had been born to young mothers.
Unfortunately, young motherhood is correlated to low IQ, which
is why their children scored so far below the national average.
Herrnstein and Murray note this problem, and claim that sampling
weights added to the NLSY make the survey sample "nationally
representative." (6) But this leads to trouble when they
attempt to analyze a growing IQ gap in children. Young motherhood
is not unusual for black women, but for white mothers it suggests
low socioeconomic status, which in turn suggests low IQ. Therefore,
the IQs of the young white and black mothers were similar…
although the IQs of their children were bound to diverge. Why?
Because black mothers, having average black IQs, would have children
with the same. But white mothers, with below-average white IQs,
would have children with IQs that would tend to rebound back towards the
higher white average. That's because trait variation is natural
in children, and if white parents are already near the bottom,
then their children, if they vary, have nowhere else to go but
up. This is technically known as "regression towards the
mean," and it is a common statistical deception. You can
get the opposite "result" by comparing average black
mothers with the smartest white mothers; the white children would
tend to drop back down to the white average, having nowhere else
to go but down. In this case, Herrnstein and Murray could have
reported that IQ gap is shrinking, not growing!
Thanks to this statistical anomaly, Herrnstein and Murray found
a four-point increase in the black/white IQ gap in their particular
sample. On this basis, they then argued that the gap is growing
everywhere. But this is certainly not the case, and the
mainstream studies remain the best indicator of the shrinking
black/white IQ gap.
Other 15-point claims
Herrnstein and Murray cite numerous other studies in their
book that produce a broad range of estimates for the black/white
IQ gap. These range from no gap to a gap of 30 points (an absurd
finding on its face, since this would mean that blacks are mentally
retarded).
To put everything in perspective, the authors provide a chart
summarizing the findings of 156 studies. (7) The results form
a bell curve of their own: the vast majority of studies have found
a difference of about 15 points, while only a few studies have
found significantly smaller or greater differences. From this
chart, one might reasonably conclude that the gap is 15 points.
But a closer look at the chart reveals some disturbing facts.
It was compiled in large part by Arthur Jensen, Frank McGurk,
R. Travis Osborne and Audrey Shuey -- all recipients of grants
from the Pioneer Fund. This is the neo-Nazi organization that
advocates eugenic policies -- namely, the phasing out of black
people. This alone does not refute the chart, of course, but one
would feel more comfortable with its objectivity if its compilers
weren't funded by overt racists.
And a look at the footnotes reveals that these fears are well-founded.
To be included in the chart, a study had to meet "basic requirements
of interpretability." These requirements included several
that many would view as fair: for example, that the studies had
to include both a black and a white sample, that the sample sizes
had to be larger than 50 for each group, etc. But the authors
then report that socioeconomic status posed "a special problem"
for them. They write:
"If a study explicitly matched subjects by SES, it was excluded.
If it simply drew its samples from a low-SES area, it was included,
even though some degree of matching had occurred." (8)
It is well-known that matching blacks and whites for socioeconomic
status will see a large reduction in the IQ gap. Researchers justifiably
dispense with such matching if they want to learn the raw differences.
But including samples from "low-SES areas" creates great
potential for mischief. Inner city schools are disproportionately
filled with poor black children, but relatively richer whites
are bussed into their schools, where they take the same IQ tests.
Furthermore, an IQ test given to a broad region like a city would
include inner-city black children and suburban white children.
Both study samples would yield unnaturally large IQ gaps.
The only way to minimize statistical errors (and deception) is
to consider nationally representative samples. As our first chart
indicates, such tests indicate a 7 to 10-point gap. For those
who accept academic achievement tests as valid proxies for IQ
tests, the gap in 1990 was about 10 points, after having been
reduced about 2.5 points per decade since 1970. (9)
Return to Overview
Endnotes:
1. K.R. Vincent, "Black/white IQ differences: Does age
make a difference?" Journal of Clinical Psychology
47, 1991, pp. 266-270.
2. Richard Herrnstein and Charles Murray, The Bell Curve,
(New York: Simon & Schuster, 1994), pp. 289-90.
3. Marilyn Elias, "Experts find fault with 'Bell Curve'"
USA Today. (No date given; probably Fall 1995.)
4. Richard Nisbett, "Race, IQ and Scientism," pp. 50-52
in Steven Fraser, ed., The Bell Curve Wars (New York: HarperCollins,
1995).
5. Herrnstein and Murray, p. 356.
6. Ibid., p. 355.
7. Ibid., pp. 276-77.
8. Ibid., p. 717.
9. Nisbett, p. 49. The academic tests used for this statistic
are listed in the chart below, which has been compiled from his
written account:
Point reduction in black/white IQ gap (1970-1990)*
Test Reduction
------------------------------------------------------
National Assessment of Education Progress 4.2 points
Scholastic Aptitude Test 5.0
National High School Studies 4.5
American College Test 4.4
Graduate Record Examination 5.7
*Total reductions have been extrapolated from different-length
studies to represent two decade period. Original lengths: NAEP,
1970-1990; SAT, 1976-1993; NHSS, 1973-1982; ACT, 1980-1991; GRE,
1980-1988.